1. Technical Field
The present invention relates to a semiconductor device package, and more particularly, to a semiconductor device package capable of reducing occurrences of faulty welding of a package base to a lid or a seal ring to be joined thereto.
2. Related Art
A semiconductor device is sealed within a package, so as to be available for use. Typically, a semiconductor device package is comprised of a metal base having a placement section on which a semiconductor device is placed, a metal frame joined to the base, a seal ring joined to an open upper face of the frame, and a metal lid joined to the seal ring. The package is formed into a box-like shape as a whole. To hermetically seal a semiconductor device within such a package, the metal lid is seam-welded to the seal ring after the semiconductor device is received in a package housing formed by the metal base, metal frame and seal ring which are silver-brazed with one another.
In the seam welding, two roller electrodes are positioned individually at one ends of two facing sides of the metal lid, with the metal frame held on the seal ring of the package housing, and the roller electrodes are pressed against the metal lid. Thereafter, the roller electrodes and the package are moved relative to one another until the roller electrodes reach the other ends of the two sides of the metal lid, while a welding current is supplied between the electrodes, whereby the lid is seam-welded at the two sides to the seal ring. Then, the remaining two sides of the lid are seam-welded to the seal ring, thereby sealing the semiconductor device within the package. As for a package not provided with a seal ring, the metal lid is seam-welded to the metal frame.
As described above, a semiconductor device package is formed into a box-like shape as a whole. In other words, the package has four corners. Seam welding of the seal ring or the metal lid to the metal frame is carried out in such a manner that only a plated layer formed in advance on a surface of the seal ring or the metal lid is caused to melt, with a constituent material of the seal ring or the lid unmelted. Therefore, seam welding is advantageous in that it can reduce influences of welding heat upon a semiconductor device received in a package. On the other hand, unstable welding conditions are liable to occur at corners of a package, and in this case, faulty welding may be caused at the corners.
Although occurrences of such faulty welding can be reduced by increasing an amount of power supply to roller electrodes, welding heat increases with increase in the amount of power supply, so that a semiconductor device accommodated in a package may receive thermal affection, causing a misalignment in the semiconductor device. As for an optical semiconductor device and an optical component that are especially required of a high alignment accuracy, a misalignment can occur for such a simple reason that a creep deformation is caused in a silver alloy, with which various portions of an optical semiconductor device are joined to one another. Thus, an increased amount of power supply in seam welding for an optical semiconductor device package may cause a misalignment in an optical semiconductor device or an optical component received therein. This indicates that it is unpractical to increase the power supply amount to eliminate welding failure. Since seam welding for a semiconductor device package is carried out in a final stage of production of semiconductor modules, welding failure entails great damage, and therefore, a reduction of occurrences of faulty welding has been strongly demanded.